Electromagnetic head



Sept. 11,.1962 A. D. SCARBROUGH 3,053,940

ELECTROMAGNETIC HEAD Filed May 20, 1957 "to vu/Je gsaura United States Patent Oilice 3,053,940 ELECTROMAGNETIC HEAD Alfred Dale Scarbrough, Palos Verdes Estates, Calif., assignor, by mesne assignments, to Thompson Rarno Wooldridge Inc;, Cleveland, Ohio, a corporation of Ohio Filed May 20, 1957, Scr. No. 660,138 4 .Claims. (Cl. 179-1003) This invention relates to an improved electromagnetic head for use in the art of magneticrecording and reproducing, and particularly to a head construction especially adapted for close association with the magnetizable surface of a rotating drum memory.

In accordance with well-known techniques, electrical pulse signals may be received by an electromagnetic head and transformed thereby into magnetic flux fields. These flux fields are caused-to produce magnetized areas upon the surface of a magnetizable medium as, for instance, the latter moves past the recording head station. Additionally, the art of reproducing electrical signals corresponding to such magnetized areas by means of an arrangement which permits the areas to be moved and to be sensed by an electromagnetic head, is also well known.

The present electromagnetic head will be presented with reference to a longitudinal recording system, i.e., one in which changes in magnetization along the direction of motion of the magnetizable medium are utilized to represent the original signals. It is to be understood, however, that the invention may also be employed in systems such as the transverse or vertical.

In conventional electromagnetic head structure, there is included a pair of identical U-shaped ferrite yoke members abutting at one pole tip and slightly spaced at the other to form an air gap. A coil is mounted on each yoke member, generally at a distance about halfway along the member. The coils are serially connected and energized by the electrical signal information to be recorded. Magnetic recording is accomplished on a moving magnetizable surface, such as that of a rotating drum memory, positioned opposite the air gap at the adjoining pole tip faces. In this arrangement, the flux effective in recording is that which issues from the gap end of the yoke in the direction of the drum; the flux issuing in the opposite direction (into the window of the yoke) and that traversing the gap, are wasted. In this type of head, non-utilizable flux amounts to at least 50% of the total available flux. Therefore, it has been found useful to construct the yoke members such that the shape of the window will be essentially rectangular, to taper the pole tips to widen the gap inwardly away from the pole faces, and to fill the gap with a non-magnetic, electrically conducting material. Such a construction results in a substantial increase in reluctance at the gap, thereby making more flux efiective in the direction of the drum.

The electromagnetic head of the present invention structurally deviates to a considerable extent from the aforementioned construction. A rectangular ferrite bar pole piece is provided in lieu of one yoke member, and the other yoke member is profiled such that, when the pole pieces are positioned to abut along a longitudinal surface, there results a long area of intimate contact (the rear gap) at their one ends, a short area of narrow separation (the front gap) at their other ends and a window area of no contact between their ends. A single excitation coil is mounted on the bar pole piece as closely as possible to the front gap and within the window. The front gap ends of the bar pole piece and the yokepole piece are machined to form a pair of flat operative surfaces capable of being precisely positioned with respect to the surface of the drum. Additionally, the electromagnetic head is provided with a. non-magnetic foil shield wound in a Patented Sept. 11 [1962 single open layer around the bar pole piece and extending from beneath the excitation coil to the machined operating surfaces. The position of the foilcontributes a shielding efiect both in the interstice between the coil and the bar pole piece and in the front gap, its thickness establishing the front gap separation. Further, such construction results close spacing between the excitation coil and the drurn and has been found quite beneficial in maximizing the intensity'of the flux field applied to the drum.

It is, erefore, an object of the invention to provide an electromagnetic head capable of improved performance in the/ recording and reproduction of electrical signals.

ltis'a further object of the inventiontoprovide an electromagnetic head construction characterized by case of assembly and adaptability to large scale economical pro duction; its partscan be fabricated from metal stampings requiring a minimum of machining forsatisfactory performance in the most critical of installations, such as in association with the revolving magnetic drum memory of a computer.

With further respect to such utilization, it will be seen that the present head is of small size, of simple configuration and is well shielded, thereby making feasible an installation in which a plurality of heads are closely spaced at the drum surface without excessive electrical or magnetic co-action or physical interference.

The features of the invention which are believed to be novel and patentable are pointed out in the appended claims. The invention, however, together with further objects and advantages thereof, may best be understood by reference to the following description of the accompanying drawings, in which:

FIGURE 1 is a front elevation and partial cross-section of the electromagnetic head of the present invention with part of a casing section broken away, shown in association with a magnetizable medium;

FIGURE 2-is a plan view of the bar pole piece of the head, showing also how the shield is applied thereto;

FIGURE 3 is a plan view of the bottom of {the internal assembly of the head. I

Although, for convenience, the invention will be shown and described with reference to recording on a magnetic drum in response to the receipt of electrical pulse signals, it is to be understood that the invention is also intended for generating electrical pulse signals by sensing recordings already existing on the drum, and further, for erasing existing recordings. 7

Referring now to FIGURE 1, a frontlelevation of the electromagnetic head, it is seen that there is provided outer casing 10 and internal assembly 11. Outer casing 10 is preferably made of some non-magnetic material,

aluminum or an alloy thereof being suitable, and comprises two identical casing sections 12a and 12b, which are hollowed to form a cavity for accommodation of internal assembly 11, cable 14, filler 34, and resin drops 36a and 36b. The abutting surfaces of sections 12a and 12b are machined for close fit, and in the complete head structure, are fastened together by pins or other means through holes 15a and 15b. The external dimensions of the assembled casings, and thus of the head, are approximately 1% inches in length, inch in width, and inch in thickness.

Internal assembly 11 includes bar pole piece 16 and yoke pole piece 18, both of which may be fabricated of a ferrite compound, steel laminations, or other material characterized by high permeability. Pole pieces 16 and 18 are preferably rectangular in cross-section, being of the same thickness, about ,5 inch, and of the same over-all length, about ,5 inch, but different in width and profile. Bar pole piece 16 is rectangular throughout its length. Yoke pole piece 18, however, is shaped such that window 19 is formed. As shown in the drawing, when pole pieces rear gap 32, window 19 is so positioned that the abutment at front gap 30 is approximately one-tenth of the length of pole pieces 16 and 18 while the abutment at rear gap 32 slightly exceeds half the length. Additionally, the construction is such that there is a separation of about 0.001 inch at front gap 30 and close contact at rear gap 32. As is well known, such an arrangement, regardless of other considerations, provides for a high magnetic reluctance across front gap 30 and a low magnetic reluctance across rear gap 32. The ends of pole pieces 16 and 18 adjoining front gap 30 are machined to a high degree of flatness to form a pair of operative surfaces 24 and 26 which are capable of close proximity, on the order of 0.001 inch, to the surface of a magnetizable medium, such as drum surface 28, moving in either direction indicated by the arrow shown. To provide a fixed relationship during operation between the ends of pole pieces 16 and 18 at front gap 30 and the ends of casing sections 12a and 12b, small drops 36a and 36b of plastic resin are placed in the interstices as shown and, after hardening, ground flush with the ends of casing sections 12a and 12b. It may be noted that operative surfaces 24 and 26 protrude slightly; this is to prevent abrasion of casing sections 12:: and 12b in operation. It may be here noted that the direction of motion of drum surface 28 with reference to the electromagnetic head is of no consequence with regard to the efficiency of recording, reproducing, or erasing of information.

The spacing between pole pieces 16 and 18 across front gap 30 is established by shield which is wound on bar pole piece 16 and extends from the end of rear gap 32 at window 19 to operative surfaces 24 and 26. Considerable latitude may be exercised in the selection of material for shield 20, the conductivity and malleability of silver makes it eminently suitable, and beryllium copper or stainless steel will also be found satisfactory.

Mounted on bar pole piece 16 at window 19 and over shield 20 and as closely as permissible to front gap is excitation coil 22, which may be a multilayer randomlywound inductor, preferably 70 turns of size 36 enameled wire. Coil 22 is connected to a conductor such as cable 14, which, in turn, is connected to a source of pulse-type electrical signals when the head is used in a recording process. The shown physical relationship between shield 20 and both front gap 30 and excitation coil 22 provides exceptional efliciency in directing flux field issue from excitation coil 22 towards drum surface 28, as will be later described.

After assembly, the interior of the electromagnetic head is completely filled with rubber-like filler 34 in order that internal assembly 11 be maintained physically stable during handling and especially during operation in which facilities for heat dissipation from the head do not prevent a temperature rise. Expansion of components in the head and possible misalignment resulting therefrom is substantially precluded by physical rigidity provided by filler 34.

The purpose of FIGURE 2 is to indicate the application of shield 20 to bar pole piece 16 as well as to present the preferred configuration for shield 20. It is here seen that shield 20 is wound on bar pole piece 16 so as to leave a slight amount of slack in the form of loops 38 at each bend. Loops 38 permit an absolutely uniform spacing for front gap 30 (FIGURE 1) in accordance with the thickness of shield 20. Such uniformity would not prevail simultaneously with complete filling of front gap 30 by shield 20 if shield 20 were wound tightly about bar pole piece 16, as a result of the formation of radii of curvature in shield 20 at the corners of bar pole piece 16. Loops 38 make possible the confining of only a flat portion of shield 20 in front gap 30. FIGURE 2 further illustrates that shield 20 is shaped to provide a bias away from operative surface 24, the purpose 'thereof being, as already mentioned, to maximize the flux field in a direction perpendicular to operative surface 24 and away from the head.

FIGURE 3 views internal assembly 11 from the direc- 20 within front gap 30. It may be noted that shield 20 is illustrated as having an opening 40. Connection to provide instead a loop with insulated ends in shield 20 may be made; the arrangement as shown, is preferred, however, as simpler with respect to assembly.

Returning now to FIGURE 1 and observing the physical relationship of shield 20 to both front gap 30 and excitation coil 22, it is obvious that shield 20 not only serves to effectuate a high magnetic reluctance at front gap 30 but also operates to similar effect at the interstice between excitation coil 22 and bar pole piece 16.

In operation, the structural characteristics of the electromagnetic head are such as to maximize the generated .flux field as follows: parallel to the longitudinal dimension of bar pole piece 16, across rear gap 32, along yoke pole piece 18, out of operative surface 26, across the interstice between the head and drum surface 28, returning through operative surface 24 to bar pole piece 16.

It will be appreciated by those skilled in the art that the novel electromagnetic head construction described above is characterized by optimum physical configuration and transducing elliciency. However, it is to be understood that the preferred embodiment of the invention is not to be considered as limitative, neither in the above description nor in the showing of the drawings, since the invention may otherwise be practiced without departing materially from the appended claims.

What is claimed is:

1. An electromagnetic head assembly of the type capable of recording, reproducing and erasing with respect to a moving magnetizable medium, comprising: a bar pole piece having a plane inner surface; a U-shaped yoke pole piece defining first, second, and third parallel inner surfaces, said first innersurface positioned in abutting relationship to a first end of said bar pole piece plane surface said third inner surface positioned in confronting relationship to a second end of said bar pole piece plane surface to form a gap therebetween, said second inner surface being substantially spaced from said bar pole piece plane surface whereby a window is defined therebetween; a coil wound on said bar pole piece and positioned within the window; a foil shield formed of conductive non-magnetic material wound on said bar pole piece as a single electrical open turn and extending under said coil and within the gap, the opening thereof being located at a surface of said bar pole piece not forming the gap, said shield being provided, where bent, with integral loops for winding on said bar pole piece, thereby to uniformly fill the gap; a non-magnetic electrically conducting housing surrounding said pole pieces, coil and foil conductor, said housing having an opening to provide protrusion of said pole pieces and foil conductor in the direction of the magnetizable medium; means to provide a fixed spacial relationship between the gap ends of said pole pieces and said housing; and an elastic filler material to provide for complete occupation of said housing.

2. The electromagnetic head assembly of claim 1 wherein the area of said first inner surface in abutting relationship with said bar pole piece is substantially greater than the area of said third inner surface in confronting relationship with said bar pole piece.

3. An electromagnetic head assembly of the type capable of recording, reproducing and erasing with respect to a moving magnetizable medium comprising: a bar pole piece having a plane inner surface; a U-shaped yoke pole piece defining first, second, and third parallel inner surfaces, said first inner surface positioned in abutting relationship to a first end of said bar pole piece plane surface, said third inner surface positioned in confronting relationship to a second end of said bar pole piece plane surface to form a gap therebetween, said second inner surface being substantially spaced from said bar pole piece plane surface whereby a window is defined therebetween; a coil wound on said bar pole piece and positioned within the window; a foil shield formed of conductive non-magnetic material wound on said bar pole piece as a single electrical open turn and extending under said coil and within the gap, the opening thereof being located at a surface of said bar pole piece not forming the gap, said shield being provided, where bent, with integral loops for winding on said bar pole piece, thereby to uniformly fill the gap.

4. The electromagnetic head assembly of claim 3 wherein the area of said first inner surface in abutting relationship with said bar pole piece is substantially greater than the area of said third inner surface in confronting relationship with said bar pole piece.

References Cited in the file of this patent UNITED STATES PATENTS Schnizel May 5, 1936 Zenner Aug. 21, 1951 Camras Oct. 21, 1952 Eckert et a1. Nov. 18, 1952 Rettinger Feb. 10, 1953 Field Nov. 24, 1953 Munroe Feb 9, 1954 Sprosty May 22, 1956 Brewer et al June 24, 1958 Hansen Sept. 16, 1958 Brower Dec. 2, 1958 Zenel et a1. July 14, 1959 

